In the related art, a vehicular automatic transmission which can form a gear shift stage having ten forward gear stages and one reverse gear stage is disclosed. For example, in a technology which is disclosed in U.S. Pat. No. 7,828,688 (Reference 1) illustrated below, by providing three single pinion type planetary gears and six engaging elements, and among these, by engaging three elements with each other, gear shift stages having ten forward gear stages and one reverse gear stage are formed.
The vehicular automatic transmission illustrated in U.S. Pat. No. 7,828,688 (Reference 1) is configured as described below. A first planetary gear which includes a first carrier linked to an output shaft can select a link between the first carrier and a second sun gear of a second planetary gear via a first clutch, and a link between a first sun gear and the second sun gear via a second clutch. In a third planetary gear which includes a third carrier linked to the output shaft, a second ring gear of the second planetary gear is linked to the third carrier, and a first ring gear of the first planetary gear is linked to a third sun gear. A second carrier of the second planetary gear can select a link with a third ring gear of the third planetary gear via a third clutch. Also, the third ring gear can select a link with a fixing member via a first brake. The first sun gear can select a link with the fixing member via a second brake. The first ring gear can select a link with the second carrier via a fourth clutch. By fastening the first carrier of the first planetary gear which is linked to the input shaft with the second sun gear of the second planetary gear by engaging the first clutch, fastening the second carrier of the second planetary gear with the third ring gear of the third planetary gear by engaging the third clutch, and fixing the second carrier with the first brake, a reverse gear shift stage makes reverse rotation of which a rotating direction is reverse to that of an input shaft to the second ring gear of the second planetary gear. Then, the reverse rotation of the input shaft is output from the output shaft which is linked to the third carrier of the third planetary gear linked to the second ring gear. In this manner, since the reverse rotation is made to the second planetary gear only by an input into the second planetary gear and by fastening the brake, the third ring gear of the third planetary gear is fixed by the first brake, and the third carrier reversely rotates. For this reason, the third sun gear passively reversely rotates, and reversely rotates at a higher speed than that of the third carrier. Since the first ring gear of the first planetary gear which is linked to the third sun gear reversely rotates, and the input rotation is input by the input shaft into the first carrier, the first sun gear of the first planetary gear is subjected to rotate at a high speed as the speed reaches the highest rotating speed in the reverse gear shift stage. Therefore, increasing the rotating speed of the first sun gear influences durability of a bearing member or the like which supports the first sun gear, and suppression of an increase in the rotating speed is required.